Method and means for distillation of low boiling point liquids



Aug. 26, 1952 P KAPlTZA 2,608,070

METHOD AND MEANS FOR DISTILLATION OF LOW BOILING POINT LIQUIDS FiledFeb. 20, 1946 Sl-IEETS-Sl-IEET 1 I I o .1, n

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as) x: i BY Pa er Z. K6791 2 Aug. 26, 1952 P. 1.. KAPITZA METHOD ANDMEANS FOR DISTILLATION OF LOW BOILING POINT LIQUIDS 2 SHEETS-SHEET 2Filed Feb. 20, 1946 MN M m WRN Patented Aug. 26, 1952 METHODAND ll/IEANSFOR DISTILLATIQN LOW BOILING POINTLIQ U IDSj Peter Leonidovitch;Kapitza, Moscow, Union of Soviet Socialist Republics ApplicationFebruary20, 1946, Serial No, 648,908 In, the. Union. of Soviet SocialistRepublics February 11, 1944 6 Claims. (Cl. 6.2. 1 23.-)

The present inventionrelates to. method and means for rectification anddistillation of liquid with low temperature boiling points.

The main difficulty encountered in the fractional distillation orrectification of liquids boiling at low temperatures such asoccur forexample in the distillation of air, water gas, or coal gas from theliquid phase consists inv liquifying the more volatile fraction.

In particular, when producing oxygen from air the greatest difiiculty isencountered in obtaining a reflux liquid of liquid nitrogen. Hithertothese difiiculties were overcome by the use of double columns (forexample, the double columns used in the Linde and Claude methods for thefractional distillation of liquid air), in which one column serves toobtain a reflux of the most volatile component, while the other servesfor the actual distillation. This method requires that the air besupplied at high pressures While the design of the apparatusnecessitates the use of additional condensers and. evaporators. Thisreduces the efliciency of the whole system considerably and requires acomplicated construction of large dimensions.

Proposals have been made in the art to obtain a reflux by compressingthe most volatile components in a compressor, the compression beingperformed at a temperature higher than the temperature at which saidcomponent leaves the column and to afford this'said' component is ledthrough a series of heat exchangers; In this connection I cite UnitedStates Patent 2,095,809 disclosing ample evidenceof the use of theabovementioned principle.

The present invention is characterised bythe direct liquefaction of themost volatile components at the cold end of the cycle by a compressor.

The, appended schematic diagrams illustrate: in Figure 1, theapparatusfor liquifying the most volatile component in the case of abinary mixture;. in Fig. 2, a variant of the system, having a secondcompressor coupled in parallelto increase the efliciency of therectifying. column, and in Fig. 3, a system for separating mixturescon-. taining three, or. more components.

For the sake of simplicity and ease in de scribing the systemsillustrated, all mechanisms 3, and by means of the-pipe 4% passes intothe expansion engine I 5lwhichmay be of the turbine typeor any machinewherein the gas. is expanded, this expansion being accompanied by theproduction of mechanical energy delivered for adequate use after'whichthe cooledand partly liquefied gas is conducted through pipe 6 to the:column. I. Themost volatile component concentrates in the upperpartot'the column, and is: removed bypipe ll and passed to the compressor 8 inwhich it is. compressed to a pressure, at which liquefaction oi thereflux occurs. Through pipefl thecompre'ssed gas-flows into the.evaporator lllsituated'atthe lower'end of thecolumn in whichthecomponent of higher boil ing point collects. The pressureat theexhaust ofthe compressor 8- ismade'such that themost volatile componentis condensed in the evaporator- It; This liquified'component is.directed through pipe having a valve l2-to the top of column: Iandflowstothebottom oflthe column 1 passing successively over thetransverse perforated platesinside the column. The separated fractiomare removed by-p pes 13' and 4 pa ing through heatexchangers 2 and 3.The eff ciency of the, fractionating column can be increasedvery simplyby the addition of other compressors working in; parallel with thefirst.

The conditionsfon condensing and evaporating the; reflux: at variouslevels in the fractionatorare in accordance with the conditionsrequisitefor improving theefiiciency of the system. Fig. 2 showsthesamearrangementas in Fig. 1 with one additional compressor. According tothe'arrangementof the apparatus shown in Fig. 2, the, gas: of which thereflux is to be made, is removed'jrom the fractionating column; at two,poi ts, .1 at the top, through p pe. I: a d one. o ewhatlow r t u h p p.The part of the. gas; removed throughpipe 7 passes through the; cycledescribed above while that portion which isremoved by pipe 25 is di"rected; throu h. a second compressor It out of- Which itis led throu hPipe: ll to the evaporator I 8 arranged intheupp r half ofthefractionating column I. The liquified gas. isled into the column throughthe pipe and valve [9,- the inlet being somewhat higher in the column Ithan the exhaust pipe 2,0. Followingthe above principle a third, fourth,and further compressors may-be added, and the more of such compressorsthereare in operation, thecloser .will. be the mode and. the higher willbe its.

The same principle may be applied to the separation of three or morecomponents from a gaseous mixture such as the argon, nitrogen and oxygenin air. A system arranged for this purpose is shown in Fig. 3, in whichthere are two fractionating columns of the type shown in Fig. 1.

The diagram shown in Fig. 3 illustrates the use of one compressor perfractionating column. It is clear, however, that the efficiency of thesystem may be improved by the addition of further compressors accordingto the system illustrated in Fig. 2.

In the case of a trinary mixture, the gas is passed through theexpansion machine 5 to column I the two less volatile componentscollecting in the evaporator ID from which they fiow through pipe 22 tothe central part of the fractionating column 2 I. In this column, thereflux is produced by means of the compressor I6 to which the gas is ledthrough pipe 20. The compressed gas passes through pipe [1 to theevaporator IS in which it is condensed, the resulting reflux liquidbeing directed through the pipe and valve l9 to the upper end oi. thefractionating column. The component of intermediate boiling point, inthis caseargon, is led through the heat exchanger 24 through pipe 23,the component of high boiling pointoxygen-leaving the system through thepipe I4 and heat exchanger 2.

It is clear from the principle illustrated in Fig. 3 that eachadditional component requires an additional fractionating column andheat exchanger for its separation from the original mixture. Thefractionators may be supplied with one or more compressors.

Obviously, the principle described above may be applied to all existingtypes of fractionating columns such as those having perforated plates,rotating discs etc. Similarly, the heat exchangers 2, 3 and 24 may be ofany existing types.

One of the advantages of the system according to the present inventionlies in the possibility of driving the compressors from the shaft of theexpansion engine. In this case, the work expended on compressing themost volatile component and consequently raising its temperature iscompensated by the temperature drop in the expansion engine and in thismanner, the temperature balance in the fractionating column is notviolated.

Another feature of the proposed system lies in the fact that the refluxis usually composed of only a part of the total quantity of the gasflowing through the expander and consequently the pressure of the gasleaving the compressor may be made higher thanthat of the gas enteringthe expander. Furthermore when the efficiencies of the compressor andexpansion engine are sufficiently high, the pressure of the mostvolatile component (nitrogen, in the case when air is being separatedinto its two main components oxygen and nitrogen) can be made higher 'atthe evaporation point of the cycle than that of the air entering thesystem. This assists in the formation of the reflux used in theiractionating column. This is a marked advantage over the systemproposed by Linde and Frenkel.

The greater density of gases at low temperatures enables greaterpressure changes to be obtained in compressors having few compressionstages (such as turbine compressors) and in expansion engines of theturbine type and consequently increases their efiiciency as 'a result ofwhich, the use of this type of compressor and expansion engine is to berecommended in installation of the proposed type.

A further increase in the efficiency of the system may be obtained byadding an auxiliary load I5 to the axle of the expansion machine asshown in Figures 1, 2 and 3. This may be a dynamo or any other powerabsorbing machine.

The method advanced in the present invention for producing a refluxliquid of the most volatile components by means of a compressor at thecold end of a cycle can be applied in practice in various ways as isobvious from the discussion of the examples given above. Furthermore itis clear that the application of the method considerably simplifies theconstruction of fractional stills, affording new possibilities to theart of low temperature distillation.

Since details of method and means for the rectification and distillationof liquid with low temperature boiling points may be modified, the scopeof the invention is defined by the claims as hereunto appended.

I claim:

1. A method of rectification and fractional distillation of liquidsboiling at low temperatures, comprising removing at least one of themost volatile fractions of the composition undergoing fractionation froma first point at the top portion of a rectification zone, compressing atleast a part of the fraction removed at a temperature levelcorresponding substantially to the temperature at the top of saidrectification zone and returning the compressed material as a refiux tothe top portion of the rectification zone,

feeding compressed gases to the rectification zone between the top andbottom thereof, expanding the gases so fed, and utilizing the mechanicalenergy released by said expansion for compressing said part of thefraction removed from the rectification zone at the first point.

2. In the rectification and fractional distillation of liquids boilingat the low temperatures, the process which comprises liquefying gaseouscomponents of normally gaseous material, ex-

panding the liquefied gas and introducing the same into a rectificationzone between the top and bottom thereof, removing at least one of themost volatile fractions from the upper portion of said zone, compressingat least a part of said fraction at a temperature level correspondingsubstantially to the temperature at the top of said rectification zone,passing the compressed material through a lower portion of therectification zone and utilizing the same for heating that portion ofthe zone, subsequently passing the compressed material to the topportion of the zone and utilizing it as a reflux therein, and utilizingmechanical energy released by the expansion of the liquefied gas tocompress the part of the fraction removed from the top portion of therectification zone.

3. Means for effecting rectification and fractional distillation ofliquids boiling at low temperatures, comprising a rectification column,an

through the evaporator, and means for leading said fraction from theevaporator and for discharging it into the top of the column.

4. Means for effecting rectification and fractional distillation ofliquids boiling at low temperatures, comprising a rectification columnhaving two evaporators arranged therein at different levels, means forleading a normally gaseous fluid and for discharging it into the columnabove said evaporators, an expander interposed in said means forutilizing the expansion of said fluid to create mechanical energy. firstand second compressors driven by said expander, first and secondconduits leading from spaced points of the rectification column abovethe point where the normally gaseous fluid is introduced directly to thecompressors respectively, a passageway connecting one of saidcompressors to one of the evaporators, another passageway connecting theother compressor to the other one of said evaporators, a thirdpassageway connecting the evaporator at the lower level to the top ofthe column, and a fourth passageway connecting the other evaporator tothe column at a point above that where the normally gaseous fluid isintroduced.

5. Means for effecting rectification and fractional distillation ofliquids boiling at low temperatures, comprising rectification columnmeans having a plurality of evaporators arranged therein at diiferentlevels, a plurality of heat exchangers, an expansion engine, conduitmeans for passing a normally gaseous fluid through said heat exchangersand the expansion engine and for discharging the same into therectification column between the top and bottom thereof and at a pointabove said evaporators, a plurality of compressors corresponding innumber to the number of the evaporators and driven by said expansionengine, passageways placing points in the rectification means above theevaporators in direct communication respectively with the re spectivecompressors, other passageways placing the compressors in communicationwith the respective evaporators, other passageways placing eachevaporator in communication with the rectification column means at apoint above that where the evaporator is located, and conduit means forleading fractions from the rectification column means through the heatexchangers.

6. Means for effecting rectification and fractional distillation ofliquids boiling at low temperatures, and containing at least threecomponents, comprising series connected rectification columns eachhaving at least one evaporator arranged therein, the number of saidrectification columns being one less than the number of componentssubjected to distillation, at least one compressor for eachrectification column, communicating with the corresponding evaporator insaid columns, an expander, heat exchangers, means for passing a normallygaseous fluid through said heat exchangers and said expander and fordischarging the same into at least one of said rectification columnsbetween the top and bottom thereof, means for leading gaseous fractionsfrom the tops of the columns directly to the compressors, means forutilizing the mechanical energy of expanding gases in the expander todrive said compressors, means for leading fluid through each evaporatorto the rectification column in which the evaporator is located and fordischarging the same into that column at a higher elevation than theevaporator, and means for passing fluid from each rectification columnthrough at least one of the heat exchangers.

PETER LEONIDOVITCH KAPITZA.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,449,291 Mewes et a1. Mar. 20,1923 1,521,115 Mewes et al. Dec. 30, 1924 1,696,558 Van Nuys Dec. 25,1928 2,095,809 Gomonet Oct. 12, 1937 2,180,435 Schlitt Nov. 21, 19392,270,852 Schuftan Jan. 27, 1942 2,355,167 Keith 1 Aug. 8, 194,4

1. A METHOD OF RECTIFICATION AND FRACTIONAL DISTILLATION OF LIQUIDSBOILING AT LOW TEMPERARTURES, COMPRISING REMOVING AT LEAST ONE OF THEMOST VOLATILE FRACTIONS OF THE COMPOSITION UNDERGOING FRACTION ATOM FROMA FIRST POINT AT THE TOP PORTION OF A RECTIFICATION ZONE, COMPRESSING ATLEAST A PART OF THE FRACTION REMOVED AT A TEMPERATURE LEVELCORRESPONDING SUBSTANTIALLY TO THE TEMPERATURE AT THE TOP OF SAIDRECTIFICATION ZONE